1. Field of the Invention
The present invention generally relates to a rocker arm of a center pivot type or an end pivot type adapted to be driven by a cam mounted on an internal combustion engine for selectively opening and closing a valve of a cylinder head and, more particularly, to the rocker arm prepared from a plate member such as a steel plate by the use of a press work.
2. Description of the Prior Art
A rocker arm utilized in a valve drive mechanism of an internal combustion engine has hitherto been manufactured by the use of a casting technique and, therefore, the manufacture of the rocker arm involves a number of problems to be solved such as those associated with considerable weight of the manufactured rocker arm, a relatively large number of manufacturing steps and a high cost of manufacture. In contrast thereto, the rocker arm of a plate type prepared from a shaped plate that is manufactured from a plate material of a relatively small thickness by the use of a press work has now come to be largely employed because of a light-weight feature, a relatively small number of manufacturing steps and a low cost of manufacture.
The rocker arm currently in use is generally available in two types; a center pivot type, in which the rocker arm is rockingly supported at a generally intermediate portion thereof, and an end pivot type in which the rocker arm is pivotally supported at one of its opposite ends through a pivot element secured to such one of the opposite ends. The rocker arm of the plate type is generally employed for both of the center pivot type and the end pivot type.
The center pivot type is of a design in which a valve driving member is adjustably fitted in a screw hole of an adjustment element formed in an arm body so that an adjustment can be made among a cam, a valve and a rocker arm. On the other hand, the end pivot type is of a design in which a pivot element is adjustably fitted in a screw hole of an adjustment element formed in an arm body so that an adjustment can be made among a cam, a valve and a rocker arm.
The center pivot type and the end pivot type differ from each other depending on which one of the valve driving member and the pivot element is used as an element to be mounted. However, both of those types employ the adjustment element and, accordingly, if the rocker arm is prepared by the use of a plate member of a relatively small thickness, a sufficient depth can hardly be obtained in the mounting hole for the adjustment element and a problem associated with securement of a sufficient strength around the mounting hole tends to arise.
By way of example, FIG. 30 illustrates the conventional center pivot type rocker arm such as disclosed in, for example, the Japanese Laid-open Patent Publication No. 2001-41011. The conventional rocker arm 51 shown therein includes an arm body 52 prepared from a single plate member by the use of a press work. The arm body 52 has a generally inverted U-shaped section defined by a pair of parallel side walls 53 and a connecting wall 54 bridging between respective upper edges of the side walls 53. One end of the connecting wall 54 that defines the adjustment element is formed with a female-threaded mounting hole 55 defined therein for adjustably receiving a valve driving member (not shown) therein. This mounting hole 55 is reinforced by formation of a cylindrical bulged portion 56 so that the valve driving member can be firmly retained. Also, when the rocker arm 51 is so designed that the respective centers of the adjustment element and a roller support structure is offset axially, the cylindrical bulged portion 56 will interfere with the side walls 53 unless any other measure is taken and, therefore, an open window 57 is defined in one of the side walls 53 on an offset side so as to avoid the interference.
While in the conventional rocker arm shown in FIG. 30 the cylindrical bulged portion 56 is formed in the mounting hole 55 in the connecting wall 54 to secure a required depth of the mounting hole 55, formation of the mounting hole 55 is complicated and time-consuming because of the cylindrical bulged portion 56 so formed. Where the offset structure is employed, the open window 57 is defined to avoid interference with the cylindrical bulged portion 56, but the amount of offset is limited only with a play afforded by the open window 57.
Also, in this conventional rocker arm, if the arm body 52 of a relatively large thickness is employed, a sufficient strength can be secured around pivot support holes 58 defined in the respective side walls 53. However, since the plate thickness of the entire arm body 52 of the generally inverted U-shaped section increases, the connecting wall 54 which does not require a relatively high strength will have a correspondingly increased thickness, resulting in inconvenience in reducing the overall weight of the arm body. In addition, the amount of material used to manufacture the arm body will unnecessarily increase.
FIG. 31 illustrates the conventional rocker arm of the end pivot type such as disclosed in, for example, the Japanese Laid-open Patent Publication No. 2001-132414. This conventional rocker arm 81 includes an arm body 82 of a generally inverted U-shaped section having one end thereof provided with an end overlap piece 83 extending in a direction lengthwise of the arm body 82, which overlap piece 83 is turned backwardly to define an adjustment element of an overlapped structure. A mounting hole 85 is defined in this adjustment element of the overlapped structure, in which a pivot member (not shown) is adjustably inserted. Since in this example, the adjustment element is of the overlapped structure, a sufficient strength can be secured around the mounting hole 85.
However, since the end overlap piece 83 has to be turned backwardly and a step of turning the end overlap piece 83 backwardly, which is separate from a step of shaping the arm body 82 so as to have a generally inverted U-shaped section, is required, the number of manufacturing steps consequently increases, resulting in increase of the manufacturing cost.
Also, in order for the mounting hole 85 to be formed after the end overlap piece 83 has been turned backwardly, the distance L from the mounting hole 85 to a bent portion at which the end overlap piece 83 is turned backwardly as shown in FIG. 31 has to be somewhat large. In other words, since a bending process is employed to turn the end overlap piece 83 backwardly, degradation of material occurs in a portion of the end overlap piece 83 and/or the connecting wall 84 adjacent the bent portion and, therefore, they are not suited to formation of the mounting hole 85. Particularly where the mounting hole 85 is employed in the form of an internally threaded screw hole, inconveniences will undoubtedly arise. For this reason, it is necessary to provide a sufficient margin which enables the arm body to overcome detrimental effects possibly brought about by the degradation of material. Since as discussed above the front end portion of the arm body 82 is required to have an increased length inclusive of the above mentioned margin, the rocker arm 81 as a whole has a correspondingly increased length, far from being manufactured compact. Even where the adjustment element of the overlapped structure defined by the end overlap piece 83 is applied to the center pivot type shown in and described with reference to FIG. 30, a similar problem associated with the lengthwise dimension as discussed above will arise.
FIG. 32 illustrates the center pivot type rocker arm suggested in, for example, the Japanese Laid-open Patent Publication No. 10-299430. A rocker arm 61 shown therein is of a generally folded structure formed by bending an elongated plate member about a substantially intermediate portion 61b thereof so as to define two side walls 63 and 64, with the bent portion 61b defining an adjustment element in which a valve driving member (not shown) is adjustably inserted.
In this conventional rocker arm of the center pivot type shown in FIG. 32, a mounting hole 75 defined in the adjustment element can be formed to have a relatively great depth, but since the arm body is defined only by the mutually confronting side walls 63 and 64, means is required to regulate the space between the side walls 63 and 64 to a predetermined or required value. It is to be noted that the side walls 63 and 64 are formed with respective cylindrical bulged portions 70 positioned around associated pivot support holes 69 and, accordingly, a sufficient strength can be secured even though the rocker arm 61 is prepared from a thin plate material. However, formation of the cylindrical bulged portions 70 is indeed time-consuming and laborious.
Also, since in the conventional rocker arm 61 shown in FIG. 32, there is no means by which the space between the side walls 63 and 64 is regulated to a predetermined or required value, an extra space regulating means is required.
While in describing the prior art believed to be pertinent to the present invention reference has been made to the center pivot type, similar problems to those discussed above equally applies even to the rocker arm of the end pivot type.
The present invention is intended to provide a rocker arm of a kind wherein a sufficient strength can be secured around a mounting hole defined in an adjustment element with a simplified manufacturing, and which is assembled less costly and light-weight with a minimized number of manufacturing steps and can have a reduced length. This object of the present invention can be achieved by the rocker arm as set forth in the appended claims.
Another object of the present invention is to provide a rocker arm of a kind wherein the amount of offset can easily be adjusted without changing the width of an arm body and only with changing a widthwise dimension of the adjustment element. A still another object of the present invention is to provide a rocker arm wherein a sufficient strength can be secured around respective pivot support portions of opposite side walls by a simplified manufacturing step.
A further object of the present invention is to facilitate an offset structure to be designed easily.
A still further object of the present invention is to provide a rocker arm of an end pivot type in which a sufficient strength can be secured in each of the opposite side walls, and which can be manufactured light-weight and less costly with a reduced number of manufacturing steps.
To these ends, the rocker arm according to any one of first to sixth aspects of the present invention is rocked by a cam to actuate a valve of an internal combustion engine and, for this purpose, is of a design in which an arm body of the rocker arm is prepared from a single plate material by means of a press work so as to be constructed of a pair of side walls opposite to each other and a connecting wall bridging between the opposite side walls.
Of the rocker arms according to the first to sixth aspects of the present invention, the rocker arm according to the first aspect of the present invention is of a center pivot type and is so constructed as follows.
The arm body has first and second ends opposite to each other and also has a pivot support portion defined at a location generally intermediate of the length of the arm body. A roller is rotatably mounted on the first end of the arm body for driving engagement with the cam, and an adjustment element is defined on the second end of the arm body. Specifically, the adjustment element is defined by an overlapped structure that includes an end overlap piece formed integrally with a side portion of the connecting wall adjacent the second end of the arm body and bent backwardly to overlap the connecting wall to thereby define the adjustment element. The adjustment element has a mounting hole defined therein for adjustably receiving therein a valve driving member.
According to the first aspect of the present invention, since the adjustment element is defined by the overlapped structure formed by overlapping the end overlap piece against the connecting wall, a sufficient depth can be secured in the mounting hole extending through the adjustment element, resulting in the securement of a sufficient strength around the mounting hole defined in the adjustment element. In such case, the adjustment element of the overlapped structure is formed by overlapping the end overlap piece against the connecting wall, processing to reinforce is easy to achieve. Also, since the adjustment element is defined by the end overlap piece extending from the side portion of the connecting wall, the dimension of the margin required to avoid a deteriorated portion in the vicinity of a bent portion occurring in a direction widthwise of the arm body can be secured in the widthwise direction of the arm body. Because of this, the overall length of the arm body will not increase to provide the overlapped structure, making the arm body compact in the lengthwise direction. With respect to the direction widthwise of the arm body, because of securement of the widthwise dimension of the roller held in rolling contact with the cam, a sufficient margin can be obtained relative to the inner diameter of the mounting hole and, therefore, there is no need to increase the width of the arm body. Also, since the rocker arm is prepared from a single plate material by the use of any known press work, it is light-weight and less costly with the number of manufacturing steps reduced.
The mounting hole referred to above may be displaced relative to a center of the connecting wall in a widthwise direction thereof. Where the offset structure is designed by such displacement, a sufficient amount of offset can be secured since no cylindrical bulged portion such as employed in the- prior art rocker arms is employed therein.
The width of the overlapped structure in a widthwise direction of the connecting wall may be increased to a value greater than that of the connecting wall. While the width of the overlapped structure defining the adjustment element need not be increased in view of a margin for providing a bending or folding, increase of the width of the overlapped structure allows the amount of offset between the adjustment element and the roller support structure to be chosen arbitrarily as desired without changing the widthwise dimension of a main portion of the arm body, but only with changing the widthwise dimension of the adjustment element. Accordingly, without accompanying a considerable increase of the weight of the rocker arm, the relatively large amount of offset can be secured.
The rocker arm according to the second aspect of the present invention is of an end pivot type and is so constructed as follows.
Specifically, the arm body of the rocker arm of the end pivot type includes a roller rotatably mounted on a portion generally intermediate of the length of the arm body for driving engagement with the cam. A valve driving member is formed in the first end of the arm body for driving engagement with the valve, and an overlapped structure is formed on the second end of the arm body. This overlapped structure includes an end overlap piece formed integrally with a portion of the connecting wall adjacent the second end of the arm body, said end overlap piece being bent backwardly to overlap the connecting wall to thereby define an adjustment element having a mounting hole defined therein for adjustably receiving therein a pivot member.
Although the rocker arm according to the second aspect of the present invention differs from that according to the first aspect of the present invention in that a member mounted on the adjustment element in the rocker arm according to the second aspect of the present invention is the pivot member, the following effects similar to those afforded by the rocker arm according to the first aspect of the present invention can be obtained. Specifically, since the adjustment element is defined by the overlapped structure formed by overlapping the end overlap piece against the connecting wall, a sufficient depth can be secured in the mounting hole in the adjustment element, resulting in the securement of a sufficient strength around the mounting hole defined in the adjustment element. In such case, the adjustment element of the overlapped structure is formed only by overlapping the end overlap piece over the connecting wall, processing to reinforce is easy to achieve. Also, since the adjustment element of the overlapped structure is formed by the end overlap piece extending from the side portion of the connecting wall, the dimension of the margin required to avoid a deteriorated portion in the vicinity of a bent portion occurring in a direction widthwise of the arm body can be secured in the widthwise direction of the arm body. Because of this, the overall length of the arm body will not increase to provide the overlapped structure. With respect to the direction widthwise of the arm body, because of securement of the widthwise dimension of the roller held in rolling contact with the cam, a sufficient margin can be obtained relative to the inner diameter of the mounting hole and, therefore, there is no need to increase the width of the arm body. Also, since the rocker arm is prepared from a single plate material by the use of any known press work, it is light-weight and less costly with the number of manufacturing steps reduced.
According to the present invention, in either of the rocker arm according to the first aspect of the present invention and that according to the second aspect of the present invention, the end overlap piece may be provided in a plural number, in which case the plural end overlap pieces are bent one at a time to overlap one above the other to thereby define the overlapped structure having three or more overlapping layers. Where the plural end overlap pieces are used to form the overlapped structure, the thickness of the overlapped structure can be increased and, hence, that of the adjustment element can have a correspondingly increased strength.
Also, the end overlap piece overlapping the connecting wall may be welded to the connecting wall and/or a free end of the end overlap piece may be inserted into an engagement opening defined in one of the side walls so that the overlapped structure defining the adjustment element can have an increased strength.
The mounting hole defined in the adjustment element may be an internally threaded hole. Where the internally threaded hole is used for the mounting hole, a portion of the arm body around the mounting hole must have a sufficient strength to secure the sufficient strength of threads forming the internally threaded hole and, for this purpose, a sufficient marginal dimension has to be secured in the vicinity of the bending portion. However, in the present invention, since the end overlap piece extends from the side portion of the connecting wall, there should arrive no problem associated with increase of, for example, the length of the arm body.
At least a portion of one or both of the side walls of the arm body may be configured to represent an overlapped structure defined by bending a portion of the plate material. Where this overlapped structure in which that portion of one or both of the side walls is bent to overlap is employed, a portion where the strength is required can be selectively reinforced and a sufficient strength can be obtained even if a relatively thin plate material is employed. In particular, in the first aspect of the present invention, that is, in the case of the rocker arm of the center pivot type, when a portion of the side wall adjacent the pivot support portion is so configured to represent the overlapped structure in which a portion of the plate material is bent to overlap, a sufficient strength of the portion of the side walls in the vicinity of the pivot support portion where the strength is required can be secured with no need to increase the plate thickness. Because of the overlapped structure employed, processing to increase the strength is much simple and easy to achieve.
The rocker arm according to the third aspect of the present invention is of a center pivot type and is so constructed as follows.
The arm body has a pivot support portion defined at a location generally intermediate of the length of the arm body, and a roller is rotatably mounted on the first end of the arm body and is engageable with the cam. An adjustment element is formed on the second end of the arm body and has a female thread defined therein, and a valve driving member having a male thread is adjustably inserted in the adjustment element with the male thread engaged with the female thread. The female thread is made up of an internally threaded hole extending through the connecting wall and a partially threaded portion defined in an inner surface of each of the opposite side walls in continuation with the internally threaded hole.
The female thread in which the valve driving member is fitted is made up of the internally threaded hole formed in the connecting wall forming a ceiling of the adjustment element of a generally inverted U-shaped section and the partially threaded portions formed respectively in the mutually confronting surfaces of the opposite side walls in continuation with the internally threaded hole and, accordingly, the male thread of the valve driving member can be threadingly engaged with the opposite side walls. Because of this, a threading strength of the female thread for receiving the valve driving member can be secured. Hence, no use of, for example, any overlapped structure or wall of an increased thickness is needed for reinforcement of the screw hole. Thus, while the number of the manufacturing steps is reduced, a sufficient strength can be secured around the threaded hole in the adjustment element and it is possible to manufacture the light-weight rocker arm at a low cost with minimized number of the manufacturing steps.
Also, since the adjustment element is defined by a reduced width portion of a generally inverted U-shaped section or a generally U-shaped section and, therefore, a necessary strength can be secured. Yet, since the inverted U-shaped section or the U-shaped section assumed by the reduced width portion defining the adjustment element is similar to that represented by the arm body, processing is easy to achieve.
In this structure, a portion of one or both of the opposite side walls adjacent the pivot support portion may be configured to represent an overlapped structure formed by bending a portion of the plate material.
Where as hereinabove described that portion of the side wall adjacent the pivot support portion is configured to represent the overlapped structure, a sufficient strength of that portion of the side walls around the pivot support portion where the strength is required can be secured with no need to increase the plate thickness. Because of the overlapped structure employed sufficiently, processing to increase the strength is much simple and easy to achieve.
The side wall of the overlapped structure may be made up of a first side wall forming plate segment continued from the connecting wall and defining that portion of the side wall adjacent the pivot support portion, and a second side wall forming plate segment extending integrally from the first side wall forming plate segment and bent to overlap the first side wall forming plate segment, with a roller support hole defined in a free end of the second side wall forming plate segment for supporting the roller. In this case, the overlapped structure may be defined only in one of the opposite side wall.
In the case of this structure, since only one of the opposite side walls represents the overlapped structure and the roller support hole is defined in the second side wall forming plate segment that is bent to overlap the first side wall forming plate segment, an offset structure can easily be obtained in which the center of the adjustment element and the center of a roller support structure are displaced in a direction of a pivot support pin.
Also, the rocker arm according to the fourth aspect of the present invention is of an end pivot type and is so constructed as follows.
The arm body of this rocker arm includes a roller rotatably mounted on a portion generally intermediate of the length of the arm body for driving engagement with the cam, and a valve driving member formed in a first end of the arm body for driving engagement with the valve. An adjustment element is defined on a second end of the arm body and has a female thread defined therein. A pivot member having a male thread is adjustably inserted in the adjustment element with the male thread engaged with the female thread. This female thread referred to above is made up of an internally threaded hole extending through the connecting wall and a partially threaded portion defined in an inner surface of each of the opposite side walls in continuation with the internally threaded hole.
The female thread in which the pivot member is fitted is made up of the internally threaded hole formed in the connecting wall forming a ceiling of the adjustment element of a generally inverted U-shaped section and the partially threaded portions formed respectively in the mutually confronting surfaces of the opposite side walls in continuation with the internally threaded hole and, accordingly, the male thread of the pivot member can engage with the opposite side walls. Therefore, no use of any overlapped structure or wall of an increased thickness is needed for reinforcement of the threaded hole. Thus, while the number of the manufacturing steps is reduced, a sufficient strength can be secured around the threaded hole in the adjustment element while the number of manufacturing steps is reduced.
Even with this structure, since the adjustment element is defined by a reduced width portion of a generally inverted U-shaped section or a generally U-shaped section and, therefore, a necessary strength can be secured. Yet, since the inverted U-shaped section or the U-shaped section assumed by the reduced width portion defining the adjustment element is similar to that represented by the arm body, processing is easy to achieve.
According to the fifth aspect of the present invention, the rocker arm is of a center pivot type and is so constructed as follows.
The arm body of the rocker arm according to the fifth aspect of the present invention has a pivot support portion defined at a location generally intermediate of the length of the arm body and a roller is rotatably mounted on a first end of the arm body and engageable with the cam while an adjustment element is formed on a second end of the arm body for adjustably receiving a valve driving member therein. At least a portion of one or both of the opposite side walls adjacent the pivot support portion is configured to represent an overlapped structure formed by bending a portion of the plate material.
According to this structure, since that portion of the side wall adjacent the pivot support portion is configured to represent the overlapped structure, a sufficient strength of that portion adjacent the pivot support portion where the strength is required can be secured with no need to increase the plate thickness. Because of this, a portion of the connecting wall where the strength requirement is relatively low will not unnecessarily increase in thickness and, therefore, while the arm body is designed to have a light-weight feature with reducing the materials used, the rocker arm can be manufactured inexpensively with the number of manufacturing steps reduced and, also a sufficient strength can be secured around the pivot support portion. Also, because of the overlapped structure employed, processing to increase the strength is much simple and easy to achieve.
Where that portion of the side wall adjacent the pivot support portion is configured to represent the overlapped structure, such overlapped structure of the side wall may be formed by providing a side overlap piece extending integrally from the side wall and then bending it to overlap the side wall. Where the use is made of the side overlap piece which is eventually bent to overlap the side wall to provide the overlapped structure, it can be accomplished with a simplified processing.
The side wall of the overlapped structure referred to above may include a first side wall forming plate segment continued from the connecting wall and defining that portion of the side wall adjacent the pivot support portion, and a second side wall forming plate segment extending integrally from the first side wall forming plate segment and bent to overlap the first side wall forming plate segment, with a roller support hole defined in a free end of the second side wall forming plate segment for supporting the roller. Even with this configuration, the overlapped structure can easily be obtained with a simplified processing Also, in the case of this configuration, since the roller is mounted on the second side wall forming plate segment, and if the overlapped structure is defined only in one of the opposite side walls, an offset structure can be obtained in which the center of the adjustment element and the center of the roller support structure are displaced in a direction of a pivot support pin.
Without the first side wall forming plate segment and the second side wall forming plate segment being tightly overlapped one above the other, they may be separated in a direction of the pivot support pin in the arm body. In such case, by suitably choosing the distance of separation between the first and second side wall forming plate segments, the amount of offset required to realize the offset structure can be adjusted as desired.
According to the sixth aspect of the present invention, the rocker arm is of an end pivot type and is so constructed as follows.
The arm body of the rocker arm according to the sixth aspect of the present invention has a roller rotatably mounted on a portion generally intermediate of the length of the arm body for driving engagement with the cam and, also, a valve driving member formed in a first end of the arm body for driving engagement with the valve while an adjustment element is formed on a second end of the arm body for adjustably receiving a pivot member therein. At least a portion of one or both of the opposite side walls adjacent the pivot support portion is configured to represent an overlapped structure formed by bending a portion of the plate material. The overlapped structure in the side wall is formed where a strength requirement is high, for example, where a mounting hole for the roller is formed and/or a lengthwise range of the side walls on which the valve driving member acts.
Even with this configuration, a sufficient strength can be obtained at a portion of the side wall where it is required, with no need to increase the plate thickness. For this reason, the thickness of a portion of the connecting wall where the strength requirement is relatively low will not increase unnecessarily and, hence, while the arm body is designed to have a light-weight feature with reducing the materials used, a sufficient strength can be secured. Also, since that portion of the side wall of the arm body is simply bent to provide the overlapped structure, the rocker arm according to the sixth aspect of the present invention is light-weight and less costly with the number of manufacturing steps reduced and, at the same time has an increased strength around a pivot support portion where the rocker arm is pivotably supported.